The present invention relates to pre-fabricated structural elements and to a method of assembling the same.
Such elements may, but need not be, reinforced concrete elements, such as pre-fabricated reinforced concrete members.
Structural combinations or assembly sets for erecting of such structures as buildings or the like, have been proposed in the art, e.g. from German Published Application No. 1,484,043, German Gebrauchsmuster No. 7,313,393 and British Patent No. 1,601,783. These disclosures are all directed to the problem of attaining stiff, bending-resistant joints in structural assemblies made by connecting pre-fabricated structural elements together. They prepare point-supporting of the elements on frusto-conical abutments. However, experience has shown that these proposals are not advantageous because the magnitude of clamping forces (i.e. retentive forces which prevent relative shifting of the elements) which can be attained in this manner is very low.
The moment acting at the juncture of such prefabricated elements resolves itself into a horizontally acting couple of forces; the direction in which these forces act relative to the juncture or joint (an inclined wedge-shaped plane) produces a force acting parallel to the joint and tending to move the elements apart from one another. This latter force can be absorbed only partially by the frictional resistance which the elements oppose to it in the region of the joint. This factor determines the limits of the degree of efficiency of this prior-art form of support because the magnitude of the frictional resistance required to obtain a state of equilibrium (i.e. for the frictional force to completely absorb the separating force) cannot be ascertained with general validity for the erection of structures.
Accordingly, a form of support must be considered to be statically favorable, wherein the frictional forces in the joint between cooperating structural elements need not be relied upon, but can instead be utilized merely as a secondary way of increasing the carrying capacity of the joint so as to enhance the structural safety.
Another disadvantage of the type of support suggested in the prior art for the structural elements is caused by a horizontally acting separating force which is generated by the vertical load. Depending upon the magnitude of the wedge angle of the support, this force may amount to a multiple of the vertical load. The order of magnitude of this separating force decisively affects the structural and economic factors involved in erecting structures of the type under discussion, as it plays a part in determining the helical reinforcement surrounding a socket, or the strength of the mantle required in a pin-and-socket joint, or the magnitude of the horizontal shear stress.
The prior-art attempts to make a pre-fabricated reinforced-concrete construction method more economical and/or technologically more advantageous by making the support or joint conditions approach those which are known from monolithic concrete-skeleton structures, are well known in the field and need not be discussed here.